To summarise: Collect Radscorpion Glands on your travels through the Wasteland or even better verse Giant Radscorpions (3 if your good enough) at the The Thorn battle arena. On average a single battle can give 10 Glands for use.

After collecting alot of Glands go to Primm (complete the quest there to unlock the Casino there) and talk to Ruby Nash, who usually walks outside the Mojave Express building near the Casino. She can convert 5 Radscorpion Glands into 5 Radscorpion Venom Casseroles. Make sure your health is not 100% (harm yourself with Dynamite, Grenade or a Mine), enter your Pipboy and eat all the casseroles you create at once (you don't need to eat and wait).

Each casserole gives 60 HP to Food. In theory you need to obtain 170 glands/casseroles from scratch to do this, but if you work The Thorn for Glands you can gain this quickly. As an added bonus you can gain XP, Caps and even do other 10000 damage achievements with different weapons (Melee, Unarmed, Guns, Energy Weapons, don't do Explosives) while beating on the Giant Radscorpions.